Diarrhea is a substantial problem for many HIV-infected persons. The causes of diarrhea in this patient group are many; they include problems with absorption, infections that may cause diarrhea, and side effects of drug that are needed to treat HIV infection or prevent opportunistic illnesses. Methods of decreasing drugs side effects are especially important now that highly active antiretroviral therapy is available that decreases viral load and increases survival. Taking these drugs without interruption is important to decrease the chances of mutations in the HIV genome that might result in drug resistance. SP-303 is an investigational agent that has been effective in decreasing diarrhea in other patient groups. This study will determine the safety and efficacy of this drug for the treatment of diarrhea in patients with AIDS.